28 Mr. J. Satterly on the Amount oj Radium 



The amount of radium which would be in radioactive 

 equilibrium with the emanation in one cubic metre of air is 

 called by Eve the Radium Equivalent. Therefore the average 

 radium equivalent on the days given in Table X. is 



^x jj. x 3-14 xlO~»x -0223 



90 4*65 



= 130xl0- 12 gm.* 



In the 1908 experiments the porcelain tubes absorbed in 

 two hours an amount 2*5 from the radium solution. The 

 silica tubes with more than 4 times the cross-section of the 

 porcelain tubes only absorb 4*65 in three hours. This looks as 

 if the charcoal tended to get saturated with the emanation, 

 so that the amount absorbed is not proportional to the time 

 of exposure. The air-readings also tend to give the same 

 conclusion for the average value of the emanation caught 

 from the air in 21 hours (deduced from the results of March, 

 April. May, June, and August) is 2'45, which is much less 

 than 7 times '8 the average value of the air caught in 3 

 hours. 



These facts suggest that the absorption of the emanation by 

 the charcoal is two-fold, one stage being quick — a surface 

 condensation, and the other much longer — a diffusion into 

 the interior, as has been discovered by McBainf for the 

 absorption of hydrogen by charcoal. 



These experiments have led to other experiments on 

 saturation which will be published in due course. 



In order to get solution readings to compare with the 



21-hours air readings, it is therefore necessary to make 



solution-exposures of 21 hours. The radium solution used 



above is too strong for this purpose, as it is wise^to keep the 



amount of emanation from the solution about equal to that 



from the air, so a solution of one-fifth strength, i. e. containing 



3'14x 10~ 9 



- gm. of radium, was made up. In calculating 



o 



the results of the experiments given in the following table 



allowance has been made for the fact that the absorptive 



power of tube B was about 10 per cent, better than that of 



tube A. (This is shown by the air-results of June and 



August.) The air-stream was kept practically constant at 



•5 litre per minute. 



* The calculation is not quite correct as no allowance is made for the 

 decay of the first portions of the emanation taken from the air, whereas 

 the formula used for the solution allows for this. The error, however, 

 is practically negligible, . 



t Phil. Ma-. Dec. 1909, - ' 



